Why are the adults concerned about Cassie in "Roll of Thunder, Hear My Cry"?
If you are asking about a specific incident, I assume that you are referring to the reaction to Cassie's odd behavior after she and her brothers sabotage the school bus. White reaction to the situation is swift, and that night Cassie witnesses night riders, the same ones who so brutally burned the Berry men, out looking for revenge. Terrified that they will suffer monstrous retribution like the Berrys, but sworn to secrecy by Stacey, Cassie mopes around the house for a week, as if she has "the whooping cough, flu, and measles all put together". Big Ma tells Mama that Cassie "ain't sleepin' right neither...and she won't hardly even go out and play" (Chapter 4).
In a larger sense, the adults are concerned about Cassie because of her naivete concerning social conditions for African Americans in the South during those times. Cassie is a passionate and impetuous child, with a clear understanding of right and wrong. When she sees blacks being subjected to constant humiliation at the hands of white people, her immediate tendency is to fight back, and she is unaware of the social reality which makes it extremely dangerous to do so. Her confrontation with Lillian Jean Simms in Strawberry is a case in point, and the injustice when Cassie is made to submit to the white girl's imperiousness is beyond her understanding. Unlike the adults, who have learned to live with indignity and injustice as a matter of survival, Cassie cannot accept the reality of the day (Chapter 5).